MagnaFlow Dyno Accuracy
I suspect the dyno was fairly close to right. The relative humidity was a bit high (this reduces air density) but air temp and atmospheric pressure were reasonable. My stock twinspark engine in a rear drive car hit 112 bhp @ 5600 rpm. My guess is that the rear drive nets a loss of 30 to 35 bhp. So, let's say it was a loss of 35 bhp; that, plus the 112 measured would be 147 bhp at the flywheel. That's darn close to the "advertised" 148 bhp @ 5800 rpm.
I think what we are seeing here is a just an example of how small seat-of-the-pants (SOP) horsepower are compared when with dyno (SAE) horsepower. It looks like it takes about 1.3 SOP horses to equal 1 SAE horse.
Now I must admit, I'm not immune to the SOP hp problem. I had expected my twinspark race engine to be showing something like 140 to 145 bhp. It didn't even get close. However, it was spitting some good sized bits of muffler baffle out the tail pipe which I'm guessing became partially blocked. Guess I should get a MagnaFlow installed!
Bruce Colby - Street = '69 1750 GTV/TS; Track = '65 SGT/TS, '89 E30, '72 914/6
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- '71 Jr. Z, '69 1750 Spider, '62 Spider